knot happening

it brings tears to my eyes sometimes when I solve a physics problem correctly. It's like surprising almost that I was mentally capable of achieving such a feat. I am perpetually scared of the impermanence of the world; the fact that who we are today is not who we will be years from now. Will I be mentally exhauasted beyond repair come June when I have to take my MCAT? Will my body be able to handle the atrocious sleeping and feeding habits I have been resorting to over the past few days to get through finals week will it all just come crashing down on me? my stomach hurts.